source: JEM-EUSO/esaf_cc_at_lal/packages/simulation/detector/tools/src/DiffusePhotonsOnPupil.cc @ 114

// ESAF : Euso Simulation and Analysis Framework
// $Id: DiffusePhotonsOnPupil.cc 2835 2009-07-16 03:22:42Z biktem $
// A.Thea created Apr, 18 2004

#include "DiffusePhotonsOnPupil.hh"
#include "OpticsFactory.hh"
#include "EsafRandom.hh"
#include "EsafSpectrum.hh"
#include <TMath.h>

ClassImp(DiffusePhotonsOnPupil)

//______________________________________________________________________________
DiffusePhotonsOnPupil::DiffusePhotonsOnPupil() {
    // ctor

    fOptics = OpticsFactory::Get()->MakeOpticalSystem();
    fThetaFOVMax = Conf()->GetNum("DiffusePhotonsOnPupil.fThetaFOVMax")
        *TMath::DegToRad();

    // calculate the entrance disc size using the last element in fAngles
    fEntranceDiscRadius = fOptics->Radius()+fThetaFOVMax*
        (fOptics->FirstLensTop()-fOptics->FirstLensBottom());

    fSpectrum = new EsafSpectrum(Conf()->GetStr("DiffusePhotonsOnPupil.fSpectrum").c_str());

    string sThDist = Conf()->GetStr("DiffusePhotonsOnPupil.fThetaDistribution").c_str();

    if (sThDist == "totaleff" ) {
        // this fuction is the inverse of the total optics efficacy as presented by
        // A.Thea at Munich EUSO General Meeting, Nov 2003
        fThetaDist = new TF1("toteff","sin(x)/pol6",0,fThetaFOVMax);

        fThetaDist->SetParameter(0,2.99368e+06);
        fThetaDist->SetParError(0,10391.8);
        fThetaDist->SetParLimits(0,0,0);
        fThetaDist->SetParameter(1,532256);
        fThetaDist->SetParError(1,98140.9);
        fThetaDist->SetParLimits(1,0,0);
        fThetaDist->SetParameter(2,-2.21992e+06);
        fThetaDist->SetParError(2,333382);
        fThetaDist->SetParLimits(2,0,0);
        fThetaDist->SetParameter(3,-2.15698e+06);
        fThetaDist->SetParError(3,778156);
        fThetaDist->SetParLimits(3,0,0);
        fThetaDist->SetParameter(4,-1.26283e+08);
        fThetaDist->SetParError(4,1.72771e+06);
        fThetaDist->SetParLimits(4,0,0);
        fThetaDist->SetParameter(5,4.02746e+08);
        fThetaDist->SetParError(5,3.47659e+06);
        fThetaDist->SetParLimits(5,0,0);
        fThetaDist->SetParameter(6,-3.87307e+08);
        fThetaDist->SetParError(6,5.62178e+06);
        fThetaDist->SetParLimits(6,0,0);

    } else if ( sThDist == "uniform" ) {
        // uniform distribution in the FOV solid angle
        fThetaDist = new TF1("uniform","sin(x)",0, fThetaFOVMax);
        fThetaDist->SetParameter(0,0);
        fThetaDist->SetParError(0,0);
        fThetaDist->SetParLimits(0,0,0);
        fThetaDist->SetParameter(1,1);
        fThetaDist->SetParError(1,0);
        fThetaDist->SetParLimits(1,0,0);
    } else if ( sThDist == "costheta" ) {
        // this distribution keeps the incident flux constant
        fThetaDist = new TF1("costheta","sin(x)*cos(x)",0, fThetaFOVMax);
    } else
        Msg(EsafMsg::Panic) << "DiffusePhotonsOnPupil: " <<
                sThDist << " unknown distribution" << MsgDispatch;


}

//______________________________________________________________________________
DiffusePhotonsOnPupil::~DiffusePhotonsOnPupil() {
    // dtor
    if (fSpectrum) delete fSpectrum; fSpectrum = 0;
    if (fThetaDist) delete fThetaDist; fThetaDist = 0;
}

//______________________________________________________________________________
Photon* DiffusePhotonsOnPupil::GetPhoton() {
    // get a new photon
    TRandom *rndm = EsafRandom::Get();
    Double_t th = fThetaDist->GetRandom(0, fThetaFOVMax);
    Double_t ph = TwoPi()*rndm->Rndm();

    Double_t rho = Sqrt(rndm->Rndm())*fEntranceDiscRadius;
    Double_t alpha = rndm->Rndm()*TwoPi();

    Double_t s_pos[3]={0,0,0};
    Double_t p_pos[3]={rho*Cos(alpha), rho*Sin(alpha),
        fOptics->FirstLensBottom()};

    fParent.Build(1,s_pos, p_pos, th, ph, fSpectrum->GetLambda(), 0, Fluorescence);
    return &(fParent.GetPhoton());
}